Preparation of polyoxymethylene dimethyl ethers by catalytic conversion of dimethyl ether with formaldehyde formed by dehydrogenation of dimethyl ether

ABSTRACT

A particularly useful process which includes the steps of providing a source of formaldehyde formed by conversion of dimethyl ether in the presence of a catalyst comprising copper and zinc; and contacting the source of formaldehyde and a predominately dimethyl ether feedstream with a heterogeneous, condensation promoting catalyst capable of hydrating dimethyl ether under conditions of reaction sufficient to form an effluent comprising water, methanol, formaldehyde, dimethyl ether, and polyoxymethylene dimethyl ethers is disclosed. Unreacted dimethyl ether is recovered from the effluent and recycled to the formation of polyoxymethylene dimethyl ethers. The resulting dimethyl ether-free liquid mixture is heated in the presence of an acidic catalyst to convert at least the methanol and formaldehyde present to polyoxymethylene dimethyl ethers. Advantageously, methylal and higher polyoxymethylene dimethyl ethers are formed and separated in a catalytic distillation column. By including in the column an anion exchange resin, an essentially acid-free product is obtained which can be used directly as a blending component, or fractionated, as by further distillation, to provide more suitable components for blending into diesel fuel.

TECHNICAL FIELD

The present invention relates to production of organic compounds,particularly polyoxymethylene dimethyl ethers, which are suitablecomponents for blending into fuel having improved qualities for use indiesel engines. More specifically, it relates to employing aheterogeneous, condensation promoting catalyst capable of hydratingdimethyl ether in conversion of dimethyl ether and formaldehyde to forma condensation effluent. A dimethyl ether-free mixture, separated formthe effluent, is heated in a catalytic distillation column to convertmethanol and formaldehyde present to methylal and higherpolyoxymethylene dimethyl ethers and separate the methylal from thehigher polyoxymethylene dimethyl ethers. Advantageously, the catalyticdistillation column has a section containing an anion exchange resinwhereby an essentially acid-free product is obtained which can be useddirectly as a blending component, or fractionated, as by furtherdistillation, to provide more suitable components for blending intodiesel fuel.

This integrated process also provides its own source of formaldehydewhich is an un-purified liquid stream derived from a mixture formed bydehydrogenation of dimethyl ether using a catalyst based on copper, zincand a member selected from the group consisting of sulfur, selenium andtellurium as catalyst components.

BACKGROUND OF THE INVENTION

Conversion of low molecular weight alkanes such as methane to syntheticfuels or chemicals has received increasing attention because lowmolecular weight alkanes are generally available from secure andreliable sources. For example, natural gas wells and oil wells currentlyproduce vast quantities of methane. Reported methods for converting lowmolecular weight alkanes to more easily transportable liquid fuels andchemical feedstocks can be conveniently categorized as direct oxidativeroutes and/or as indirect syngas routes. Direct oxidative routes convertlower alkanes to products such as methanol, gasoline, and relativelyhigher molecular weight alkanes. In contrast, indirect syngas routestypically involve production of synthesis gas as an intermediateproduct.

Routes are known for converting methane to dimethyl ether. For example,methane is steam reformed to produce synthesis gas. Thereafter, dimethylether and methanol can be manufactured simultaneously from the synthesisgas, as described in U.S. Pat. No. 4,341,069 issued to Bell et al. Theyrecommend a dimethyl ether synthesis catalyst having copper, zinc, andchromium co-precipitated on a gamma-alumina base. Alternatively, methaneis converted to methanol, and dimethyl ether is subsequentlymanufactured from methanol by passing a mixed vapor containing methanoland water over an alumina catalyst, as described in an article byHutchings in New Scientist (Jul. 3, 1986) 35.

Formaldehyde is a very important intermediate compound in the chemicalindustry. The extreme reactivity of the formaldehyde carbonyl group andthe nature of the molecule as a basic building block has madeformaldehyde an important feedstock for a wide variety of industriallyimportant chemical compounds. Historically, formaldehyde has found itslargest volume of application in the manufacture of phenol-formaldehyderesins, urea-formaldehyde resins and other polymers. Pure formaldehydeis quite uncommon since it polymerizes readily. It was usually obtainedas an aqueous solution such as formalin, which contains only about 40percent formaldehyde. However, more recently, formaldehyde is usuallytransported as an item of commerce in concentrations of 37 to 50 percentby weight. A solid source of formaldehyde called paraformaldehyde isalso commercially available.

Because of the reactivity of formaldehyde, its handling and separationrequire special attention. It is a gas above -19° C. and is flammable orexplosive in air at concentrations of about 7 to about 12 mol percent.Formaldehyde polymerizes with itself at temperatures below 100° C. andmore rapidly when water vapor or impurities are present. Sinceformaldehyde is usually transported in aqueous solutions of 50 percentby weight or lower concentration, producers have tended to locate closeto markets and to ship the methanol raw material, which has a smallervolume.

It is known that some reactions may be carried out by means of catalyticdistillation. In catalytic distillation, reaction and separation arecarried out simultaneously in a distillation column with internal and/orexternal stages of contact with catalyst.

In U.S. Pat. No. 4,215,011, Smith, Jr. discloses a method for theseparation of an isoolefin, preferably having four to six carbon atoms,from streams containing mixtures thereof with the corresponding normalolefin, wherein the mixture is fed into a reaction-distillation columncontaining a fixed-bed, acidic cation exchange resin and contacted withthe acidic cation exchange resin to react the isoolefin with itself toform a dimer and the dimer is separated from the normal olefin, theparticulate catalytic material, i.e., the acidic cation exchange resin,being contained in a plurality of closed cloth pockets, which pocketsare arranged and supported in the column by wire mesh.

In U.S. Pat. No. 4,443,559, Smith, Jr. discloses a catalyticdistillation structure which comprises a catalyst component associatedintimately with or surrounded by a resilient component, which componentis comprised of at least 70 vol. percent open space for providing amatrix of substantially open space. Examples of such resilient componentare open-mesh, knitted, stainless wire (demister wire or an expandedaluminum); open-mesh, knitted, polymeric filaments of nylon, Teflon,etc.; and highly-open structure foamed material (reticulatedpolyurethane).

In U.S. Pat. No. 5,113,015, David A. Palmer, K. D. Hansen and K. A.Fjare disclose to a process for recovering acetic acid from methylacetate wherein the methyl acetate is hydrolyzed to methanol and aceticacid via catalytic distillation.

In German Democratic Republic DD 245 868 A1 published May 20, 1987 inthe text submitted by the applicant, preparation of methylal is carriedout by reaction of methanol with trioxane, formalin or paraformaldehydein the presence of a specific zeolite. Autoclave reactions of 1 to 8hours are described using a zeolite of the "LZ40 type" with a ratio ofsilicon dioxide to alumina ratio of 78 at temperatures from 493 to 543K. Methylal content of the product as high as 99.8 percent (withoutmethanol) is reported for trioxane at 523 K for 3 hours. Reactionpressures did not exceed 5 Mpa in the autoclave. Neither conversions norselectivity are reported.

In U.S. Pat. No. 4,967,014, Junzo Masamoto, Junzo Ohtake and MamoruKawamura describe a process for formaldehyde production by reactingmethanol with formaldehyde to form methylal, CH₃ OCH₂ OCH₃, and thenoxidizing the resulting methylal to obtain formaldehyde. In the methylalformation step, a solution containing methanol, formaldehyde and waterwas brought into solid-liquid contact with a solid acid catalyst, and amethylal-rich component was recovered as a distillate. This processemploys reactive distillation performed using a distillation column andmultireaction units. The middle portion of the distillation column wasfurnished with stages from which the liquid components were withdrawnand pumped to the reactor units, which contained solid acid catalyst.The reactive solutions containing the resulting methylal were fed to thedistillation column, where methylal was distilled as the overheadproduct.

Polyoxymethylene dimethyl ethers are the best known members of thedialkyl ether polymers of formaldehyde. While diethyl and dipropylpolyoxymethylene ethers have been prepared, major attention has beengiven to the dimethyl ether polymers. Polyoxymethylene dimethyl ethersmake up a homologous series of polyoxymethylene glycol derivativeshaving the structure represented by use of the type formula indicatedbelow:

    CH.sub.3 O(CH.sub.2 O).sub.n CH.sub.3

Chemically, they are acetals closely related to methylal, CH₃ OCH₂ OCH₃,which may be regarded as the parent member of the group in which n ofthe type formula equals 1. They are synthesized by the action ofmethanol on aqueous formaldehyde or polyoxymethylene glycols in thepresence of an acidic catalyst just as methylal is produced. Onhydrolysis they are converted to formaldehyde and methanol. Like otheracetals, they possess a high degree of chemical stability. They are notreadily hydrolyzed under neutral or alkaline conditions, but areattacked by even relatively dilute acids. They are more stable than thepolyoxymethylene diacetates.

Due to the relatively small differences in the physical properties(melting points, boiling points, and solubility) of adjacent members inthis series, individual homologs are not readily separated. However,fractions having various average molecular weight values have beenisolated. The normal boiling point temperature of a fraction havingaverage n of 2 in the type formula is reported as 91° to 93° C. Boilingpoints at atmospheric pressure calculated from partial pressureequations range from 105.0° C. for n of 2, to 242.3° C. for n of 5.(Walker, Joseph Frederic, "Formaldehyde", Robert E. Krieger PublishingCo., issued as No. 159 of American Chemical Society Monograph series(1975), pages 167-169)

Polyoxymethylene dimethyl ethers are prepared in laboratory scale byheating polyoxymethylene glycols or paraformaldehyde with methanol inthe presence of a trace of sulfuric or hydrochloric acid in a sealedtube for 15 hours at 150° C., or for a shorter time (12 hours) at 165°to 180° C. Considerable pressure is caused by decomposition reactions,which produce carbon oxides, and by formation of some dimethyl ether.The average molecular weight of the ether products increases with theratio of paraformaldehyde or polyoxymethylene to methanol in the charge.A high polymer is obtained with a 6 to 1 ratio of formaldehyde (aspolymer) to methanol. In these polymers, the n value of the type formulaCH₃ O(CH₂ O)_(n) CH₃ is greater than 100, generally in the range of 300to 500. The products are purified by washing with sodium sulfitesolution, which does not dissolve the true dimethyl ethers, and may thenbe fractionated by fractional crystallization from various solvents.

U.S. Pat. No. 2,449,469 in the names of W. F. Gresham and R. E. Brooksreported obtaining good yields of polyoxymethylene dimetbyl etherscontaining 2 to 4 formaldehyde units per molecule. This procedure iscarried out by heating methylal with paraformaldehyde or concentratedformaldehyde solutions in the presence of sulfuric acid.

In the past, various molecular sieve compositions, natural andsynthetic, have been found to be useful for a number of hydrocarbonconversion reactions. Among these are alkylation, aromatization,dehydrogenation and isomerization. Among the sieves which have been usedare Type A, X Y and those of the MFI crystal structure as shown in"Atlas of Zeolite Structure Types," Second Revised Edition, 1987,published on behalf of the Structure Commission of the InternationalZeolite Associates and incorporated by reference herein. Representativeof the last group are ZSM-5 and AMS borosilicate molecular sieves.

Prior art developments have resulted in the formation of many syntheticcrystalline materials. Crystalline aluminosilicates are the mostprevalent and, as described in the patent literature and in thepublished journals, are designated by letters or other convenientsymbols. Exemplary of these materials are Zeolite A (Milton, in U.S.Pat. No. 2,882,243), Zeolite X (Milton, in U.S. Pat. No. 2,882,244),Zeolite Y (Breck, in U.S. Pat. No. 3,130,007), Zeolite ZSM-5 (Argauer,et al., in U.S. Pat. No. 3,702,886), Zeolite ZSM-11 (Chu, in U.S. Pat.No. 3,709,979), Zeolite ZSM-12 (Rosinski, et al., in U.S. Pat. No.3,832,449), and others.

It is well known that internal combustion engines have revolutionizedtransportation following their invention during the last decades of the19th century. While others, including Benz and Gottleib Wilhelm Daimler,invented and developed engines using electric ignition of fuel such asgasoline, Rudolf C. K. Diesel invented and built the engine named forhim which employs compression for autoignition of the fuel in order toutilize low-cost organic fuels. Development of improved diesel enginesfor use in automobiles has proceeded hand-in-hand with improvements indiesel fuel compositions, which today are typically derived frompetroleum. Modern high performance diesel engines demand ever moreadvanced specification of fuel compositions, but cost remains animportant consideration.

Even in newer, high performance diesel engines combustion ofconventional fuel produces smoke in the exhaust. Oxygenated compoundsand compounds containing few or no carbon-to-carbon chemical bonds, suchas methanol and dimethyl ether, are known to reduce smoke and engineexhaust emissions. However, most such compounds have high vapor pressureand/or are nearly insoluble in diesel fuel, and they have poor ignitionquality, as indicated by their cetane numbers. Furthermore, othermethods of improving diesel fuels by chemical hydrogenation to reducetheir sulfur and aromatics contents, also causes a reduction in fuellubricity. Diesel fuels of low lubricity may cause excessive wear offuel injectors and other moving parts which come in contact with thefuel under high pressures.

Recently, U.S. Pat. No. 5,746,785 in the names of David S. Moulton andDavid W. Naegeli reported blending a mixture of alkoxy-terminatedpoly-oxymethylenes, having a varied mixture of molecular weights, withdiesel fuel to form an improved fuel for autoignition engines. Twomixtures were produced by reacting paraformaldehyde with (i) methanol or(ii) methylal in a closed system for up to 7 hours and at a temperaturesof 150° to 240° C. and pressures of 300 psi to 1,000 psi to form aproduct containing methoxy-terminated poly-oxymethylenes having amolecular weight of from about 80 to about 350 (polyoxymethylenedimethyl ethers). More specifically, a 1.6 liter cylindrical reactor wasloaded with a mixture of methanol and paraformaldehyde, in molar ratioof about 1 mole methanol to 3 moles paraformaldehyde, and in a secondpreparation, methylal (dimethoxymethane) and paraformaldehyde werecombined in a molar ratio of about 1 mole methylal to about 5 molesparaformaldehyde. In the second procedure, a small amount of formicacid, about 0.1 percent by weight of the total reactants, was added as acatalyst. The same temperatures, pressures and reaction times aremaintained as in the first. Disadvantages of these products include thepresence of formic acid and thermal instability of methoxy-terminatedpoly-oxymethylenes under ambient pressure and acidic conditions.

There is, therefore, a present need for catalytic processes to prepareoxygenated organic compounds, particularly polyoxymethylene dimethylethers, which do not have the above disadvantages. An improved processshould be carried out advantageously in the liquid phase using asuitable condensation-promoting catalyst system, preferably a molecularsieve based catalyst which provides improved conversion and yield. Suchan improved process which converts lower value compounds to higherpolyoxymethylene dimethyl ethers would be particularly advantageous.Dimethyl ether is, for example, less expensive to produce than methanolon a methanol equivalent basis, and its condensation to polyoxymethylenedimethyl ethers does not produce water as a co-product.

The base diesel fuel, when blended with such mixtures in a volume ratioof from about 2 to about 5 parts diesel fuel to 1 part of the totalmixture, is said to provide a higher quality fuel having significantlyimproved lubricity and reduced smoke formation without degradation ofthe cetane number or smoke formation characteristics as compared to thebase diesel fuel.

This invention is directed to overcoming the problems set forth above inorder to provide Diesel fuel having improved qualities. It is desirableto have a method of producing a high quality diesel fuel that has betterfuel lubricity than conventional low-sulfur, low-aromatics diesel fuels,yet has comparable ignition quality and smoke generationcharacteristics. It is also desirable to have a method of producing suchfuel which contains an additional blended component that is soluble indiesel fuel and has no carbon-to-carbon bonds. Furthermore, it isdesirable to have such a fuel wherein the concentration of gums andother undesirable products is reduced.

SUMMARY OF THE INVENTION

Economical processes are disclosed for production of a mixture ofoxygenated organic compounds which are suitable components for blendinginto fuel having improved qualities for use in compression ignitioninternal combustion engines (diesel engines).

According to the present invention, there is now provided a continuousprocess for catalytic production of oxygenated organic compounds,particularly polyoxymethylene dimethyl ethers. More specifically,continuous processes of this invention include contacting a source offormaldehyde and a predominately dimethyl ether feedstreain comprisingdimethyl ether and methanol with a condensation promoting catalystcapable of hydrating dimethyl ether, in a form which is heterogeneous tothe feedstream, under conditions of reaction sufficient to form aneffluent of the condensation comprising water, methanol, formaldehyde,dimethyl ether, one or more polyoxymethylene dimethyl ethers having astructure represented by the type formula

    CH.sub.3 O(CH.sub.2 O).sub.n CH.sub.3

in which formula n is a number from 1 to about 10.

For this aspect of the invention, suitable condensation-promotingcatalysts include at least one member of the group consisting ofmolecular sieves. A preferred class of molecular sieve is crystallinemetallosilicates exhibiting the MFI crystal structure, such ascrystalline aluminosilicates and crystalline borosilicates. Morepreferably the molecular sieve is crystalline aluminosilicate exhibitingthe MFI crystal structure with a silicon-to-aluminum atomic ratio of atleast 10, or the molecular sieve is crystalline borosilicate exhibitingthe MFI crystal structure, and has the following compositions in termsof mole ratios of oxides:

    0.9±0.2 M.sub.2 /.sub.n O:B.sub.2 O.sub.3 :YSiO.sub.2 :ZH.sub.2 O,

wherein M is at least one cation having a valence of n, Y is between 4and about 600, and Z is between 0 and about 160.0.

In another aspect, this invention provides continuous processes whichfurther comprise fractionating the effluent of the condensation toobtain an overhead stream which is predominantly dimethyl ether, and anessentially dimethyl ether-free bottom stream comprising formaldehyde,methanol and at least methylal. Preferably at least a portion of theoverhead stream containing dimethyl ether is recycled to contacting withthe condensation-promoting catalyst.

According to a further aspect of this invention, the essentiallydimethyl ether-free bottom stream comprising formaldehyde, methanol andat least methylal is heated with an acidic catalyst, which isheterogeneous to the feedstream, under conditions of reaction sufficientto convert formaldehyde and methanol present to methylal and higherpolyoxymethylene dimethyl ethers.

Preferably, the heating of the bottom stream with the acidic catalystemploys at least one catalytic distillation column with internal and/orexternal stages of contact with the acidic catalyst, and internal zonesto separate the methylal from the higher polyoxymethylene dimethylethers.

Suitable acidic catalysts include at least one member of the groupconsisting of bentonites, montmorillonites, cation-exchange resins, andsulfonated fluoroalkylene resin derivatives, preferably comprises asulfonated tetrafluoroethylene resin derivative. A preferred class ofacidic catalysts comprises at least one cation-exchange resin of thegroup consisting of styrene-divinylbenzene copolymers, acrylicacid-divinylbenzene copolymers, and methacrylic acid-divinylbenzenecopolymers. Preferably, the heating of the bottom stream with the acidiccatalyst employs at least one distillation column with internal and/orexternal stages of contact with the acidic catalyst.

Advantageously, the mixture of polyoxymethylene dimethyl ethers iscontacted with an anion exchange resin to form an essentially acid-freemixture. Contacting with the anion exchange resin is preferably carriedout within a section of the catalytic distillation column below thestages of contact with the acidic catalyst to form an essentiallyacid-free mixture.

In a preferred embodiment of the invention the essentially acid-freemixture of polyoxymethylene dimethyl ethers is fractionated within asection of the distillation column below the stages of contact with theacidic catalyst to provide an aqueous side-stream which is withdrawnfrom the distillation column, and an essentially water-free mixture ofhigher molecular weight polyoxymethylene dimethyl ethers (values of ngreater 1) which is withdrawn from the distillation column near itsbottom. Advantageously, at least a portion of the aqueous side-stream isused for recovery of an aqueous formaldehyde solution in an adsorptioncolumn.

In another aspect this invention is an integrated process wherein thesource of formaldehyde is formed by a process comprising continuouslycontacting dimethyl ether in the vapor phase with a catalyticallyeffective amount of a catalyst consisting of copper, zinc and a memberselected from the group consisting of sulfur, selenium and tellurium ascatalyst components at elevated temperatures to form a gaseousdehydrogenation mixture comprising formaldehyde, dimethyl ether,dihydrogen and carbon monoxide; cooling the gaseous dehydrogenationmixture with an adsorption liquid and adsorbing formaldehyde therein;and separating the resulting liquid source of formaldehyde from agaseous mixture comprising dihydrogen and carbon monoxide.

Preferably the resulting liquid source of formaldehyde contains about 30to about 85 percent by weight formaldehyde in methanol solutioncontaining less than 5 percent water, and is recovered by using at leastone continuous adsorption column with cooling to temperatures in a rangedownward from about 100° C. to 25° C.

For a more complete understanding of the present invention, referenceshould now be made to the embodiments illustrated in greater detail inthe accompanying drawing and described below by way of examples of theinvention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic flow diagram depicting a preferred aspect of thepresent invention for continuous catalytic production ofpolyoxymethylene dimethyl ethers by chemical conversion of dimethylether and formaldehyde in which unreacted dimethyl ether is recoveredfrom the effluent for recycling, and a resulting dimethyl ether-freeliquid mixture is heated in a catalytic distillation column withinternal stages of contact to convert formaldehyde and methanol presentto methylal and higher polyoxymethylene dimethyl ethers. This reactionmixture is contacted with an anion exchange resin to form an essentiallyacid-free product mixture and fractionated to provide suitablecomponents for blending into diesel fuel. The source of formaldehyde inthe integrated process depicted in FIG. 1 is a stream of formaldehyde inmethanol derived from dehydrogenation of dimethyl ether.

GENERAL DESCRIPTION

The improved processes of the present invention employ a heterogeneous,condensation promoting catalyst capable of hydrating dimethyl ether inconversion of dimethyl ether and formaldehyde to form a condensationeffluent. In general, after the feedstream is passed over the catalystit will contain a mixture of organic oxygenates at least one of which isof higher molecular weight than the starting dimethyl ether. Forexample, effluent mixtures can comprise water, methanol, formaldehyde,dimethyl ether, methylal and other polyoxymethylene dimethyl ethershaving a structure represented by the type formula

    CH.sub.3 O(CH.sub.2 O).sub.n CH.sub.3

in which formula n is a number ranging between 1 and about 15,preferably between 1 and about 10. More preferably the mixture containsa plurality of polyoxymethylene dimethyl ethers having values of n in arange from 2 to about 7. Conditions of reaction include temperatures ina range from about 50° to about 300° C., preferably in a range fromabout 1500 to about 250° C.

Stoichiometry of this condensation may be expressed by the followingequations;

    CH.sub.3 OCH.sub.3 +n CH.sub.2 O→CH.sub.3 O(CH.sub.2 O).sub.n CH.sub.3

    2CH.sub.2 OH+m CH.sub.2 O→CH.sub.3 O(CH.sub.2 O).sub.m CH.sub.3 +H.sub.2 O

which may be combined as in the following equation when n is equal to m;

    CH.sub.3 OCH.sub.3 +2CH.sub.3 OH +2nCH.sub.2 O→2CH.sub.3 O(CH.sub.2 O).sub.n CH.sub.3 +H.sub.2 O

As shown above, the synthesis of methylal and higher polyoxymethylenedimethyl ethers from dimethyl ether, methanol, and formaldehyde is areversible reaction that yields water as a co-product. Under certainconditions at least a portion of the water may be consumed in adehydrogenation reaction expressed by the following equations;

    CH.sub.3 OCH.sub.3 +CH.sub.3 OH+H.sub.2 O→3CH.sub.2 O+3H.sub.2

and

    CH.sub.3 OCH.sub.3 +H.sub.2 O←→2CH.sub.3 OH

Sources of dimethyl ether useful herein are predominantly dimethylether, preferably at least about 80 percent dimethyl ether by weight,and more preferably about 90 percent dimethyl ether by weight. Suitabledimethyl ether sources may contain other oxygen containing compoundssuch as alkanol and/or water, preferably not more than about 20 percentmethanol and/or water by weight, and more preferably not more than about15 percent methanol and/or water by weight.

According to the present invention, the ratio of formaldehyde todimethyl ether in the feedstreams is any mole ratio which results in theproduction of the desired oxygenated organic compound. The ratio offormaldehyde to dimethyl ether is preferably between about 10:1 andabout 1:10 moles. The ratio of formaldehyde to dimethyl ether ispreferably between about 5:1 and about 1:5 moles. More preferably, theratio of formaldehyde to dimethyl ether is between about 2: 1 and about1:2 moles.

The process can be performed at any temperature and pressure at whichthe reaction proceeds. Preferred temperatures are between about 20° andabout 150° C., with between about 90° and about 125° C. being morepreferred. The most preferred temperatures are between about 115° andabout 125° C.

The pressure can be atmospheric or super-atmospheric pressure. Preferredpressures are, according to the present invention, between about 1 andabout 100 atmospheres, with between about 15 and about 25 atmospheresbeing most preferred.

The reaction mixture feed gas flow rate, expressed as gas hourly spacevelocity, can be between about 50 and about 50,000 hr⁻¹, mostpreferably, between about 100 and about 2,000 hr⁻¹. Un-converteddimethyl ether can be recovered from the mixture by methods well knownin the art. One particularly desirable method is the use of distillationof the condensed product.

The process of this invention can be performed in either a fixed orfluid bed reactor, using either continuous or batch processing methods.It is preferred to use a fixed bed reactor and a continuous mode ofoperation.

Broadly, according to the present invention, a catalyst system isprovided which comprises at least one molecular sieve, preferably acrystalline metallosilicate exhibiting the MFI crystal structure.Generally the crystalline metallosilicate is combined with active orinactive materials, synthetic or naturally occurring zeolites, as wellas inorganic or organic materials which would be useful for binding thecrystalline metallosilicate. Other well-known materials include mixturesof silica, silica-alumina, alumina sols, clays, such as bentonite orkaolin, or other binders well known in the art. The crystallinemetallosilicate can also be mixed intimately with porous matrixmaterials, such as silica-magnesia, silica-alumina, silica-thoria, orsilica-titania. The crystalline metallosilicate content can varyanywhere from a few up to 100 percent by weight of the total finishedproduct. Typical catalytic compositions contain about 5 percent to about80 percent by weight of the crystalline metallosilicate

Generally, the term "molecular sieve" includes a wide variety ofpositive ion-containing crystalline materials of both natural andsynthetic varieties. They are generally characterized as crystallinealuminosilicates, although other crystalline materials are included inthe broad definition. The crystalline aluminosilicates are made up ofnetworks of tetrahedra of SiO₄ and AlO₄ moieties in which the siliconand aluminum atoms are cross-linked by the sharing of oxygen atoms. Theelectrovalence of the aluminum atom is balanced by the use of positiveions such as alkali metal or alkaline earth metal cations.

Zeolitic materials useful herein, both natural and synthetic, have beendemonstrated in the past to have catalytic capabilities for manyhydrocarbon processes. Zeolitic materials, often referred to asmolecular sieves, are ordered porous crystalline aluminosilicates havinga definite structure with large and small cavities interconnected bychannels. The cavities and channels throughout the crystalline materialare generally uniform in size allowing selective separation ofhydrocarbons. Consequently, these materials in many instances have cometo be classified in the art as molecular sieves and are utilized, inaddition to the selective adsorptive processes, for certain catalyticproperties. The catalytic properties of these materials are alsoaffected, to some extent, by the size of the molecules which are allowedselectively to penetrate the crystal structure, presumably to becontacted with active catalytic sites within the ordered structure ofthese materials.

Manufacture of the ZSM materials utilizes a mixed base system in whichsodium aluminate and a silicon-containing material are mixed togetherwith sodium hydroxide and an organic base, such as tetrapropylammoniumhydroxide and tetrapropylammonium bromide, under specified reactionconditions to form the crystalline aluminosilicate.

A preferred class of useful molecular sieves, according to the presentinvention, are crystalline borosilicate molecular sieves disclosed incommonly assigned U.S. Pat. No. 4,268,420, U.S. Pat. No. 4,269,813, U.S.Pat. No. 4,292,457, and U.S. Pat. No. 4,292,458 to Marvin R. Klotz,which are incorporated herein by reference.

Suitable for use according to the present invention are, broadly,crystalline borosilicates which comprise a molecular sieve materialhaving the following compositions in terms of mole ratios of oxides:

    0.9±0.2M.sub.2/n O: B.sub.2 O.sub.3 :YSiO.sub.2 :ZH.sub.2 O,

where M is at least one cation having a valence of n, Y is between 4 andabout 600, and Z is between 0 and about 160.

Embodiments of such borosilicate provide an X-ray diffraction patterncomprising the following X-ray diffraction lines:

    ______________________________________                                                             Assigned                                                   d (Å) Strength                                                          ______________________________________                                               11.2 ± 0.2 W-VS                                                       10.0 ± 0.2 W-MS                                                            5.97 ± 0.07 W-M                                                            3.82 ± 0.05 VS                                                             3.70 ± 0.05 MS                                                             3.62 ± 0.05 M-MS                                                           2.97 ± 0.02 W-M                                                            1.99 ± 0.02 VW-M                                                         ______________________________________                                    

wherein the assigned strengths correspond to the following values ofrelative peak heights:

    ______________________________________                                        Assigned Strength  Relative Peak Height                                       ______________________________________                                        VW                 less than 10                                                 W 10-19                                                                       M 20-39                                                                       MS 40-70                                                                      VS greater than 70                                                          ______________________________________                                    

and "d" represents interplanar spacings, expressed in terms of Angstromunits. A range of assigned strengths comprises all strengths between thelimits shown.

Embodiments of these borosilicates are prepared by the method whichcomprises: (1) preparing a mixture containing an oxide of silicon, anoxide of boron, a hydroxide of an alkali metal or an alkaline earthmetal, an alkyl ammonium cation or a precursor of an alkyl ammoniumcation, and water; and (2) maintaining said mixture at suitable reactionconditions to effect formation of said borosilicate, said reactionconditions comprising a reaction temperature within the range of about25° to about 300° C., a pressure of at least the vapor pressure of waterat the reaction temperature, and a reaction time that is sufficient toeffect crystallization.

After recovering a dimethyl ether-free mixture form the condensationeffluent, the mixture is heated in a catalytic distillation column withan acidic catalyst, which is heterogeneous to the feedstream, underconditions of reaction sufficient to convert formaldehyde and methanolpresent to methylal and higher polyoxymethylene dimethyl ethers.Examples of the solid acidic catalyst for use in the present inventioninclude cation exchange resins, sulfonated fluoroalkylene resinderivatives, and crystalline aluminosilicates.

Cation exchange resins that can be used in the present invention may becarboxylated or sulfonated derivatives, but sulfonated derivatives arepreferred because of the high reaction yield that can be attained. Ionexchange resins that can be used may be gel-type cation exchange resinsor macroporous (macroreticular) cation-exchange resins, but the latteras exemplified by Amberlite 200C of Organc Co, Ltd. and Lewalit SP112 ofBayer A.G. are preferred because of the high reaction yield that can beattained. Specific examples of useful ion exchange resins include astyrene-divinylbenzene copolymer, an acrylic acid-divinylbenzenecopolymer, a methacrylic acid-divinylbenzene copolymer, etc.

A sulfonated tetrafluoroethylene resin derivative (trade name, Naflon H)is preferably used as a sulfonated fluoroalkylene resin derivative.

The most desirable of these solid acidic catalysts are macroreticularcation exchange resins having sulfonate groups.

According to an integrated process of the invention a source offormaldehyde is formed by subjecting dimethyl ether in the vapor phaseto hydration and dehydrogenation in the presence a catalyticallyeffective amount of a catalyst consisting of copper, zinc and a memberselected from the group consisting of sulfur, selenium and tellurium ascatalyst components at elevated temperatures to form a gaseousdehydrogenation mixture comprising formaldehyde, dimethyl ether,dihydrogen and carbon monoxide; cooling the gaseous dehydrogenationmixture to predominantly condense dimethyl ether, and adsorbformaldehyde therein; and separating the resulting liquid source offormaldehyde from a mixture comprising dihydrogen and carbon monoxide.Preferably the catalyst components copper, zinc and selenium ortellurium as catalyst components are used in an atomic ratios of1:0.05-0.5:0.01-0.5 with tbe proviso that the amount zinc is at leastequal to the amount of selenium or tellurium, and more preferably ratiosof 1:0.05-0.5:0.05-0.4.

Preparations of suitable catalysts for conversion to formaldehyde ofdimethyl according to the invention are described in, for example, U.S.Pat. No. 4,014,939, U.S. Pat. No. 4,054,609, and U.S. Pat. No. 4,354,045which patents are specifically incorporated herein in their entirety byreference.

The catalyst used in the present invention may be prepared by any one ofconventional procedures known to those skilled in the art, for example,precipitation method, thermal decomposition method, or deposition anddrying method. Any of these procedures may be properly selected based onthe raw material to be used.

Suitable raw materials for catalyst useful in the present inventioninclude a copper salt of a mineral acid such as copper nitrate, copperchloride, copper sulfate, copper sulfite, copper hydroxide, copperoxide, basic copper carbonate, metallic copper, and the like as a sourceof copper; a zinc salt of a mineral acid such as zinc nitrate, zincchloride, zinc sulfate, zinc sulfite, zinc hydroxide, zinc oxide,metallic zinc and the like as a source of zinc; and selenic acid,selenious acid, selenium oxide, or metallic selenium and the like as asource of selenium. Further, zinc selenide, zinc selenate, zincselenite, and the like may be used as a source of both zinc andselenium, and copper selenide may be used as a source of both copper andselenium.

Such catalysts can be prepared for example, by kneading copper oxidewith zinc oxide and tellurium dioxide (and/or selenium dioxide and/orammonium sulfate) in the presence of water, drying the mixture at 130°C. and then pressing it to form pills, with or without admixture of acarrier. Suitable raw materials may be formed to a particle having adesired shape which may be tablet, sphere or the like and the averagediameter of the particles thus formed should be more than 1 mm,preferably 2 to 5 mm. Catalyst particles are then reduced in a reductiveatmosphere, for example, in two steps, first at a temperature of 100° to300° C., preferably 150° to 250° C. for more than 0.2 hour, preferably0.5 to 1 hour and then at the temperature of 500° to 750° C., preferably600° to 700° C. for more than 0.1 hour, preferably 0.5 to 1 hour.

In the oxide catalyst of the type mentioned, the copper oxide iscompletely or partially reduced to metallic copper, during use, by thehydrogen formed on dehydrogenation of methanol. In some cases it isadvantageous to reduce the catalyst prior to use, for example withgaseous hydrogen at 200 ° to 600° C.

The process may be carried out with the catalysts in the form of a fixedbed in the reaction vessel, for example a tubular reactor. However, afluidized bed can also be used.

The statement that the catalysts according to the invention are capableof dehydrogenation dimethyl ether to formaldehyde is not to be taken toimply that processes according to the invention (hydration anddehydrogenation) actually proceeds via such a reaction mechanism.

In the present method, dimethyl ether may be used alone, or methanol anddimethyl ether can be used in admixture with each other to produceformaldehyde.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to better communicate the pre sent invention, still anotherpreferred aspect of the invention is depicted schematically in FIG. 1.Referring now to FIG. 1, a mixture containing dimethyl ether insubstantially liquid form is unloaded, for example from a road tanker(not shown), into dimethyl ether storage vessel 12 which supplies chargepump 14 through conduit 13. Charge pump 14 transfers the liquid dimethylether through conduit 16 into manifold 22 which is in flow communicationwith an inlet of catalytic reactor 20. Formaldehyde in dimethyl ether issupplied through conduit 18 to manifold 22. Catalytic reactor 20contains a catalyst which has a condensation-promoting action and iscapable of hydrating dimethyl ether. Preferred catalysts are based up ona suitable molecular sieve.

It should be apparent that effluent from the catalytic reactor is avaluable product in itself. A portion of the stream can optionally bediverted from catalytic reactor 20 for delivery to a destination (notshown) where stream may subsequently be separated to recover, forexample, dimethyl ether, formaldehyde, methylal and/or otherpolyoxymethylene dimethyl ethers. The stream can alternatively beutilized as a source of feed stock for chemical manufacturing.

The effluent stream from catalytic reactor 20 is transferred throughconduits 23 and 26, by means of pump 24, and into ether recovery column30, where unreacted dimethyl ether is separated from the effluent streamto form a resulting liquid mixture of condensation products containingany unreacted formaldehyde. A dimethyl ether fraction is taken overheadthrough conduit 32 and into condenser 34 where a liquid condensate isformed. A suitable portion of the liquid condensate is refluxed intocolumn 30 through conduits 35 and 36 while another portion of thecondensate is supplied to manifold 22 through conduits 37 and 39, bymeans of pump 38, and into catalytic reactor 20.

Conduit 28 supplies pump 40 with liquid from the bottom of column 30. Asuitable portion of the liquid stream from the bottom of column 30 istransferred through conduits 41 and 42, by means of pump 40, and intoreboiler 43 which is in flow communication with the bottom of the columnthrough conduit 44. A liquid stream from the bottom of column 30 istransferred through conduit 45 into reactive distillation column 50,where simultaneous chemical reaction and multicomponent distillation arecarried out coextensively in the same high efficiency, continuousseparation apparatus. Optionally, a stream containing methanol fromstorage vessel 46 may by fed into the reactive distillation column 50and/or source of methanol advantageously is admixed with the bottomstream from column 30 and fed into reactive distillation column 50.Charge pump 48 transfers methanol in substantially liquid form into thereactive distillation column 50 through conduits 47 and 49.

Solid acidic catalyst is present in the reactive distillation column 50to allow solutions containing water, methanol, formaldehyde, methylaland one or more other polyoxymethylene dimethyl ethers to be broughtinto solid-liquid contact counter-currently with the catalyst to formproducts including methylal and higher molecular weight polyoxymethylenedimethyl ethers. More volatile reaction products are taken overhead fromthe high efficiency separation apparatus, whereas water and lessvolatile reaction products are carried down the high efficiencyseparation apparatus.

The overhead vapor stream from reactive distillation column 50 istransferred through conduit 52 into condenser 54. A suitable portion ofcondensate from condenser 54 is refluxed into reactive distillationcolumn 50 through conduits 55 and 56. A product stream containingmethylal is transferred through conduit 57 to product storage (notshown). Conduit 59 supplies pump 60 with liquid containing highermolecular weight polyoxymethylene dimethyl ethers from the bottom ofcolumn 50. A suitable portion of liquid from the bottom of column 50 istransferred, by means of pump 60, through conduits 62 and 63 intoreboiler 64 which is in flow communication with the bottom of the columnby means of conduit 66. A product stream containing higher molecularweight polyoxymethylene dimethyl ethers is transferred through conduit68 to product storage (not shown). Preferably, an anion exchange resinis disposed within a section of the distillation column below the stagesof contact with the acidic catalyst to form an essentially acid-freemixture.

An aqueous side stream containing low levels of unreacted formaldehydeand/or methanol is discharged from column 50 through conduit 58.

In the formaldehyde preparation aspect of the invention which isdescribed herein below, gaseous dimethyl ether is dehydrogenated in thepresence of catalytically effective amount of a catalyst consisting ofcopper, zinc and tellurium or selenium as catalyst components. Referringnow to the upper portion of FIG. 1, a mixture containing dimethyl etherin substantially liquid form is supplied from dimethyl ether storagevessel 12 to pump 14 through conduit 13. Dimethyl ether feedstream forformation of formaldehyde is transferred into formaldehyde reactor 90through conduit 92, heat exchanger 104, and conduit 94.

Formaldehyde reactor 90 contains particulate dehydrogenation catalystdisposed in a plurality of tubes of a vertical heat exchanger which ismaintained at temperatures from about 500° to 750° C. by circulation ofheating fluid to the shell side of formaldehyde reactor 90 throughconduit 88 from furnace 80. Heating fluid is returned to furnace 80through conduits 96 and 86 by means of pump 84. Natural gas or othersuitable fuel is supplied to furnace fuel manifold 82 through conduit 74from fulel supply 72. As described below, at least a portion of theco-product hydrogen is used as fuel for combustion with air in furnace80.

In this embodiment of the invention, CuZnTeO/Al₂ O₃ or CuZnSeO/Al₂ O₃catalyzes the conversion of dimethyl ether to formaldehyde by areversible dehydrogenation reaction at temperatures in a range fromabout 500° to 750°, preferably in a range from about 600° to 700° C.:

    CH.sub.3 OCH.sub.3 +H.sub.2 O←→2CH.sub.2 O+2H.sub.2

Gaseous effluent from formaldehyde reactor 90 is transferred throughconduit 102, cooled against the reactor feedstream in exchanger 104 andthen passed through conduit 106 into an adsorption tower 100 whereformaldehyde and dimethyl ether are separated from a mixture of gaseousco-products including hydrogen, methane, and oxides of carbon.Adsorption tower 100 contains a high efficiency packing or other meansfor contacting counter-currently the gaseous stream with an adsorptionliquid. Formaldehyde in methanol from the bottom of the adsorption toweris circulated in a pump-around to a lower section of the tower throughconduits 112 and 116, cooler 120, and conduit 118 by means of pump 114.Methanol is supplied to an upper section of the adsorption separationtower through conduit 122 by means of pump 48. Overhead temperatures arein a range of about 15° to about 55° C., preferably about 20° to about40° C.

A gaseous overhead stream including hydrogen, methane, and oxides ofcarbon is transferred through conduit 124 and into furnace fuel manifold82 by means of blower 126. Preferably the elevated temperatures aremaintained in a range from about 500° to about 750° C. using a source ofheat derived at least in part from this gaseous mixture, comprisingdihydrogen and carbon monoxide, by combustion thereof. As neededadditional fuel such as natural gas is supplied to manifold 82 from asuitable fuel source 72 through conduit 74.

As previously described, a portion of the formaldehyde in methanolsolution is transferred through conduit 18 and manifold 22 intocatalytic reactor 20. Formaldehyde solution from the adsorption tower isgenerally from about 30 to about 85 percent by weight formaldehyde inmethanol solution containing less than about 5 percent water.

In view of the features and advantages of the continuous catalyticprocesses for direct condensation of formaldehyde and dimethyl ether toform a mixture containing methylal and higher polyoxymethylene dimethylethers in accordance with this invention, as compared to the knownmethanol condensation systems previously used, the following examplesare given.

EXAMPLES 1 to 3

In Examples 1, 2 and 3 a crystalline borosilicate catalyst exhibitingthe MFI crystal structure was used to convert a predominately dimethylether feedstream and a liquid feedstream of aqueous formaldehyde inmethanol. Effluent of the condensation reactor comprised water,methanol, formaldehyde, dimethyl ether, methylal and higherpolyoxymethylene dimethyl ethers having a structure represented by thetype formula

    CH.sub.3 O(CH.sub.2 O).sub.n CH.sub.3

in which formula n is a number from 1 to about 7.

Crystalline borosilicate molecular sieve in the form of an extrudate(1/16 inch) was calcined overnight at 500° C. The calcined extrudate wascrushed and sieved to 18-40 mesh. A tubular quartz reactor was chargedwith 3.27 grams (5 cc) of the sieved particles. The tubular quartzreactor (approx. 10 mm inside diameter) was equipped with a quartzthermowell terminating at about the midpoint of the catalyst bed.

A liquid feed solution was prepared in a pressurized 50 mL autoclaveusing 11.13 grams of paraformaldehyde (95%), 15.94 grams of methanol,and 1.80 grams of water. Contents of the autoclave were stirred andheated to temperatures of 130° to 140° C. for 1 hour, and then cooled.The resulting solution was fed by a syringe pump into a preheat zoneabove the catalyst bed. Using mass flow controllers, a gas feed mixtureof dimethyl ether and nitrogen was also fed to the top of the reactor.

Liquid products from the reactor were collected in a cool (0° C.) 25 mLflask for subsequent weighing and GC analysis. Gases exiting thecollection flask were analyzed by on-line GC using both TCD and FIDdetectors. Samples of liquid products were collected during samplingintervals of 2 hours over an approximately 16 hour period of operation.Gas analyses were obtained by GC during each sampling interval.

Two samples were collected while temperature of the catalyst bed wascontrolled to three progressively higher temperatures. Each sample wasabout 7 grams. Operating conditions and results are summarized in TablesI, II and III.

Net conversion of the methoxy moiety (Net MeO, percent) is an indicationof the conversion of groups regardless of origin, i.e., both methanol(MeOH) which has one MeO per mole and dimethyl ether (DME) which has twoMeO per mol. Net MeO may be expressed as follows: ##EQU1##

EXAMPLE 4

In this example an acidic catalyst was used to convert a liquidfeedstream of formaldehyde in methanol under conditions which allowedgas-liquid contacting of the solid catalyst (trickle bed operation).Effluent of the condensation comprised water, methanol, formaldehyde,dimethyl ether, methylal and higher polyoxymethylene dimethyl ethers.

The acidic catalyst was a proton exchanged sulfonic acid based ionexchange resin. This polymeric material is a Bronstead (protic) acid. Atubular quartz reactor was charged with 5 cc of acidic catalystparticles. The tubular quartz reactor (approx. 10 mm inside diameter)was equipped with a quartz thermowell terminating at about the midpointof the catalyst bed.

A liquid feed solution was prepared in a pressurized 50 mL autoclaveusing 7.42 grams of paraformaldehyde (95%/) and 15.93 grams of methanol.Contents of the autoclave were stirred and heated to temperatures of130° to 140° C. for 1 hour, and then cooled. The resulting solution wasfed by a syringe pump into a preheat zone above the catalyst bed. Usingmass flow controllers, a gas feed mixture of dimethyl ether and nitrogenwas also fed to the top of the reactor.

Liquid products from the reactor were collected in a cool (0° C.) 25 mLflask for subsequent weighing and GC analysis. Gases exiting thecollection flask were analyzed by on-line GC using both TCD and FIDdetectors. Operating conditions and results are summarized in Table IV.

EXAMPLE 5

In this example an acidic catalyst was used to convert a mixture offormaldehyde in methanol under conditions which allowed liquidcontacting of the solid catalyst. A liquid feed solution was prepared ina pressurized 50 mL autoclave using 7.4 grams of paraformaldehyde (95%)and 15.9 grams of methanol. Contents of the autoclave were stirred andheated to temperatures of 130° to 140° C. for 1 hour, and then cooled.The autoclave was opened and charged with 1.0 gram of catalyst. Contentsof the autoclave were heated to reaction temperature for 2 to 3 hourswith stirring. After cooling to ambient temperature and settling, thesupernatant liquid was sampled for GC analysis and formaldehydetitration analysis. Results are summarized in Table V.

EXAMPLE 6

Products of several condensation runs were composited, and the compositevacuum filtered through a medium glass frit. A 90 gram aliquot offiltrate was shaken with 20 grams of basic ion-exchange resin beads(DOWEX 66) which were then allowed to settle for one hour. The resultingsupernatant liquid was then gravity filtered through a medium paperfilter. A suitable amount (54 grams) of molecular sieve type 3A, whichhad been activated by calcination at about 538° C., was mixed into thefiltrate, and the mixture allowed to stand overnight at ambienttemperatures. Liquid was separated from the sieve by vacuum filtrationthrough a medium glass frit. A 45.97 gram aliquot of this acid-free, dryfiltrate was charged to a small distillation apparatus consisting of a100 mL 3-neck flask, a fractionating column and condenser. The chargewas distilled into eight overhead fractions which were collected attemperature cuts according to the following schedule.

    ______________________________________                                        Schedule of Overhead and Bottom Temperatures                                    Fraction         Temperatures, ° C.                                  Number         Overhead Bottom                                                ______________________________________                                        1              42 to 46 70 to 94                                                2 47 to 76  95 to 109                                                         3 77 to 94 110 to 118                                                         4  95 to 100 119 to 127                                                       5 101 to 107 128 to 136                                                       6 108 to 112 137 to 146                                                       7 113 to 123 147 to 162                                                       8 124 to 150 163 to 174                                                     ______________________________________                                    

White solids (possibly paraformaldehyde) were observed in the column andcondenser during cuts 2 through 4, but not thereafter. Composition ofthe distilled fraction and bottoms are given in Table VI.

EXAMPLES 7 and 8

In these Examples a catalyst of copper, zinc and selenium was used atseveral elevated temperatures to convert a liquid feedstream of aqueousmethanol and a gaseous feedstream of dimethyl ether, nitrogen anddihydrogen. Effluent of the fixed bed reactor was a gaseousdehydrogenation mixture including formaldehyde, dimethyl ether,dihydrogen and carbon monoxide.

A tubular quartz reactor was charged with 9.27 grams (5 cc) of theCuZnSe particles which had been sieved to 18-40 mesh. The tubular quartzreactor (approx. 10 mm inside diameter) was equipped with a quartzthermowell terminating at about the midpoint of the catalyst bed.

A liquid feed solution was prepared using 13.06 grams of water and 17.33grams of methanol. The resulting solution was fed by a syringe pump intoa preheat zone above the catalyst bed. Using mass flow controllers, agaseous feedstream of 26.9 percent by volume dimethyl ether, 6.62 volumepercent nitrogen and a balance of dihydrogen was also fed to the top ofthe reactor.

Liquid products from the reactor were collected in a cool (0° C.) 25 mLflask for subsequent weighing and GC analysis. Gases exiting thecollection flask were analyzed by on-line GC using both TCD and FIDdetectors. Samples of liquid products were collected during samplingintervals of 40 and 80 minutes over an approximately 6 hour period ofoperation. Gas analyses were obtained by GC during each samplinginterval.

Samples were collected while temperature of the catalyst bed wascontrolled to temperatures of about 600° C. Each sample was about 2.5 or7 grams. Operating conditions and results are summarized in Tables VIIand VIII.

For the purposes of the present invention, "predominantly" is defined asmore than about fifty percent. "Substantially" is defined as occurringwith sufficient frequency or being present in such proportions as tomeasurably affect macroscopic properties of an associated compound orsystem. Where the frequency or proportion for such impact is not clear,substantially is to be regarded as about twenty per cent or more. Theterm "essentially" is defined as absolutely except that small variationswhich have no more than a negligible effect on macroscopic qualities andfinal outcome are permitted, typically up to about one percent.

                  TABLE I                                                         ______________________________________                                        Conversion of Feedstreams at about 100° C.                               Using a Crystalline Borosilicate Catalyst Exhibiting the MFI                  Crystal Structure                                                           ______________________________________                                        Temperature, ° C.                                                                         100      101                                                 Run Time, min 95 155                                                          Gas Feed, mol percent                                                         Nitrogen 32.925 32.925                                                        DME 67.075 67.075                                                             Liquid Feed, weight percent                                                   Methanol 55.20 55.20                                                          Formaldehyde 38.55 38.55                                                      Water 6.25 6.25                                                               Feed Rates                                                                    Gas scc/min 34.1 34.1                                                         Liquid mL/min 0.00756 0.00756                                                 Conversions, mole percent                                                     Methanol 67.15 66.96                                                          DME 4.36 2.71                                                                 Net MeO 28.20 27.10                                                           Formaldehyde 78.84 78.84                                                      Selectivities, percent                                                        Gases                                                                         CO 0 0                                                                        CO.sub.2 0 0                                                                  Liquids                                                                       Methylal 80.548 78.269                                                        HPE 0.750 0.751                                                               DME/MeOH 5.38 5.44                                                            Carbon Balance 92.57 93.39                                                  ______________________________________                                    

where MeOH is methanol, HPE is higher polyoxymethylene dimethyl etherswhich are CH₃ O(CH₂ O)_(n) CH₃ having n greater than 1, MeO is methoxymoiety, and DME is dimethyl ether.

                  TABLE II                                                        ______________________________________                                        Conversion of Feedstreams at about 130° C.                               Using a Crystalline Borosilicate Catalyst Exhibiting the MFI                  Crystal Structure                                                           ______________________________________                                        Temperature, ° C.                                                                         132      131                                                 Run Time, min 245 305                                                         Gas Feed, mol percent                                                         Nitrogen 32.925 32.925                                                        DME 67.075 67.075                                                             Liquid Feed, weight percent                                                   Methanol 55.20 55.20                                                          Formaldehyde 38.55 38.55                                                      Water 6.25 6.25                                                               Feed Rates                                                                    Gas scc/min 34.1 34.1                                                         Liquid mL/min 0.00756 0.00756                                                 Conversions, mole percent                                                     Methanol 53.59 53.68                                                          DME 5.12 4.75                                                                 Net MeO 23.52 23.33                                                           Formaldehyde 86.71 86.71                                                      Selectivities, percent                                                        Gases                                                                         CO 0 0                                                                        CO.sub.2 0.095 0.086                                                          Liquids                                                                       Methylal 64.480 64.699                                                        HPE 0.323 0.326                                                               DME/MeOH 3.48 3.50                                                            Carbon Balance 91.63 91.53                                                  ______________________________________                                    

Where MeOH is methanol, HPE is higher polyoxymethylene dimethyl etherswhich are CH₃ O(CH₂ O)_(n) CH₃ having n greater than 1, MeO is methoxymoiety, and DME is dimethyl ether.

                  TABLE III                                                       ______________________________________                                        Conversion of Feedstreams at about 160° C.                               Using a Crystalline Borosilicate Catalyst Exhibiting the MFI                  Crystal Structure                                                           ______________________________________                                        Temperature, ° C.                                                                         164      160                                                 Run Time, min 345 400                                                         Gas Feed, mol percent                                                         Nitrogen 32.925 32.925                                                        DME 67.075 67.075                                                             Liquid Feed, weight percent                                                   Methanol 55.20 55.20                                                          Formaldehyde 38.55 38.55                                                      Water 6.25 6.25                                                               Feed Rates                                                                    Gas scc/min 34.1 34.1                                                         Liquid mL/min 0.00756 0.00756                                                 Conversions, mole percent                                                     Methanol 34.82 35.19                                                          DME 7.45 1.12                                                                 Net MeO 17.84 14.05                                                           Formaldehyde 90.59 90.59                                                      Selectivities, percent                                                        Gases                                                                         CO 0 0                                                                        CO.sub.2 0.370 0.317                                                          Liquids                                                                       Methylal 42.970 43.410                                                        HPE 0.094 0.096                                                               DME/MeOH 2.37 2.54                                                            Carbon Balance 92.40 94.76                                                  ______________________________________                                    

Where MeOH is methanol, HPE is higher polyoxymethylene dimethyl etherswhich are CH₃ O(CH₂ O)_(n) CH₃ having n greater than 1, MeO is methoxymoiety, and DME is dimethyl ether.

                  TABLE IV                                                        ______________________________________                                        Trickle Bed Conversion of Feedstreams Using an Ion Exchange                     Resin Based Catalyst Exhibiting Bronstead Acid Sites                        ______________________________________                                        Temperature, ° C.                                                                         71                                                           Feed Rates                                                                    Gas scc/min 10                                                                Liquid mL/min 0.0756                                                          Conversions, mole percent                                                     Methanol 87.04                                                                Formaldehyde 92.27                                                            Selectivities, percent                                                        Methylal 97.78                                                                HPE 1.77                                                                    ______________________________________                                    

Where HPE is higher polyoxymethylene dimethyl ethers which are CH₃ O(CH₂O)_(n) CH₃ having n greater than 1.

                  TABLE V                                                         ______________________________________                                        Liquid Phase Conversion Using an Ion Exchange Resin Based                       Catalyst Exhibiting Bronstead Acid Sites                                    ______________________________________                                        Temperature, ° C.                                                                         67                                                           Conversions, mole percent                                                     Methanol 73.38                                                                Formaldehyde 77.91                                                            Selectivities, percent                                                        Methylal 88.20                                                                HPE 6.03                                                                    ______________________________________                                    

                                      TABLE VI                                    __________________________________________________________________________    COMPOSITION OF OVERHEAD FRACTIONS AND BOTTOMS                                      Compound                 CH.sub.3 O(CH.sub.2 O).sub.n CH.sub.3 where                                   the value of n is:                              Fraction                                                                           Methylal                                                                            Methanol                                                                            Hemiacetals                                                                          Trioxane                                                                            2   3   4   5   6   7                           __________________________________________________________________________    Starting                                                                           49.95 0.0   0.69   2.42  22.60                                                                             12.42                                                                             6.40                                                                              3.15                                                                              1.45                                                                              0.61                          1 97.21 0.95 0.05 0.0 0.46 0 0 0 0 0                                          2 93.83 2.52 0.38 0.0 2.84 0 0 0 0 0                                          3 20.81 12.92 8.85 2.39 54.80 0.17 0 0 0 0                                    4 3.24 11.12 6.40 4.49 74.19 0.57 0 0 0 0                                     5 0.56 8.47 2.29 5.83 82.07 0.78 0 0 0 0                                      6 0.40 3.10 0.16 7.21 88.05 1.08 0 0 0 0                                      7 0.43 0.99 0.0 9.38 86.60 2.55 0.05 0 0 0                                    8 0.32 0.47 0.0 11.77 82.98 4.37 0.08 0 0 0                                   Bottoms 0.29 0.02 0.0 0.54 1.10 49.49 26.19 13.05 6.34 2.96                 __________________________________________________________________________

                  TABLE VII                                                       ______________________________________                                        Dehydrogenation of Dimethyl Ether at about 600° C.                       Using a Catalyst of Copper, Zinc and Selenium                               ______________________________________                                        Temperature, ° C.                                                                         599      596                                                 Run Time, min 40 80                                                           Gas Feed, mol percent                                                         Nitrogen 6.62 6.62                                                            DME 26.90 26.90                                                               Dihydrogen 66.48 66.48                                                        Liquid Feed, weight percent                                                   Methanol 57.03 57.03                                                          Water 42.97 42.97                                                             Feed Rates                                                                    Gas scc/min 135 135                                                           Liquid mL/min 0.07563 0.07563                                                 Conversions, mole percent                                                     Methanol 55.62 58.29                                                          DME 17.33 14.87                                                               Net MeO 27.75 26.69                                                           Selectivities, percent                                                        CO 3.66 3.27                                                                  CO.sub.2 13.94 15.08                                                          Formaldehyde 66.29 67.15                                                      Methylal 0 0                                                                  HPE 0.311 0.312                                                               DME/MeOH 6.07 6.75                                                            Carbon Balance 92.57 93.39                                                  ______________________________________                                    

Where HPE is higher polyoxymethylene dimethyl ethers which are CH₃ O(CH₂O)_(n) CH₃ having n greater than 1, MeO is methoxy moiety, and DME isdimethyl ether.

                  TABLE VIII                                                      ______________________________________                                        Dehydrogenation of Dimethyl Ether at about 600° C.                       Using a Catalyst of Copper, Zinc and Selenium                               ______________________________________                                        Temperature, ° C.                                                                         599      596                                                 Run Time, min 210 275                                                         Gas Feed, mol percent                                                         Nitrogen 6.62 6.62                                                            DME 26.90 26.90                                                               Dihydrogen 66.48 66.48                                                        Liquid Feed, weight percent                                                   Methanol 57.03 57.03                                                          Water 42.97 42.97                                                             Feed Rates                                                                    Gas scc/min 135 135                                                           Liquid mL/min 0.07563 0.07563                                                 Conversions, mole percent                                                     Methanol 51.17 51.70                                                          DME 13.64 16.33                                                               Net MeO 23.63 25.95                                                           Selectivities, percent                                                        CO 2.78 2.80                                                                  CO.sub.2 15.15 17.31                                                          Formaldehyde 70.63 68.01                                                      Methylal 0 0                                                                  HPE 0.318 0.306                                                               DME/MeOH 5.96 5.83                                                          ______________________________________                                    

Where HPE is higher polyoxymethylene dimethyl ethers which are CH₃ O(CH₂O)_(n) CH₃ having n greater than 1, MeO is methoxy moiety, and DME isdimethyl ether.

That which is claimed is:
 1. A process for the catalytic production of amixture of oxygenated organic compounds suitable as a blending componentof fuel for use in compression ignition internal combustion engines,which process comprises providing a source of formaldehyde formed by theconversion of dimethyl ether in the presence of a catalyst comprisingcopper, zinc and a member select from the group consisting of sulfur,selenium and tellurium; and contacting the source of formaldehyde and apredominately dimethyl ether feedstream with a condensation promotingcatalyst capable of hydrating dimethyl ether, in a form which isheterogeneous to the feedstream, under conditions of reaction sufficientto form an effluent of condensation mixture comprising water, methanol,formaldehyde, dimethyl ether, one or more polyoxymethylene dimethylethers having a structure represented by the formulaCH₃ O(CH₂ O)_(n) CH₃where n is a number from 1 to about
 10. 2. The process according toclaim 1 wherein the conditions of reaction include temperatures in arange from about 50° to 130° C., and the condensation promoting catalystcapable of hydrating dimethyl ether comprises at least one member of thegroup consisting of molecular sieves.
 3. The process according to claim2 wherein the molecular sieve is crystalline metallosilicate exhibitingthe MFI crystal structure.
 4. The process according to claim 2 whereinthe molecular sieve is crystalline aluminosilicate exhibiting the MFIcrystal structure and has a silicon-to-aluminum atomic ratio of at least10.
 5. The process according to claim 2 wherein the molecular sieve iscrystalline borosilicate exhibiting the MFI crystal structure, and hasthe following compositions in terms of mole ratios of oxides:

    0.9±0.2 M.sub.2/n O:B.sub.2 O.sub.3 :YSiO.sub.2 :ZH.sub.2 O,

wherein M is at least one cation having a valence of n, Y is between 4and about 600, and Z is between 0 and about
 160. 6. The processaccording to claim 2 which further comprises fractionating the effluentof the condensation to obtain an overhead stream, which is predominantlydimethyl ether, and an essentially dimethyl ether-free bottom streamcomprising formaldehyde, methanol and at least methylal, and heating thebottom stream with an acidic catalyst, which is heterogeneous to thefeedstream, under conditions of reaction sufficient to convertformaldehyde and methanol present to methylal and higherpolyoxymethylene dimethyl ethers.
 7. The process according to claim 6wherein the heating of the bottom stream with the acidic catalystemploys at least one catalytic distillation column with internal and/orexternal stages of contact with the acidic catalyst, and internal zonesto separate methylal from higher polyoxymethylene dimethyl ethers. 8.The process according to claim 6 wherein a source of methanol is admixedwith the bottom stream, and the heating of the resulting admixture withthe acidic catalyst employs at least one catalytic distillation columnwith internal and/or external stages of contact with the acidiccatalyst, and internal zones to separate methylal from higherpolyoxymethylene dimethyl ethers.
 9. The process according to claim 7wherein the mixture of polyoxymethylene dimethyl ethers is contactedwith an anion-exchange resin to form an essentially acid-free mixture.10. The process according to claim 7 wherein the mixture ofpolyoxymethylene dimethyl ethers is contacted with an anion-exchangeresin disposed within a section of the distillation column below thestages of contact with the acidic catalyst to form an essentiallyacid-free mixture.
 11. The process according to claim 10 wherein theessentially acid-free mixture of polyoxymethylene dimethyl ethers isfractionated within a section of the distillation column below thestages of contact with the acidic catalyst to provide an aqueousside-stream which is withdrawn from the distillation column, and anessentially water-free mixture of polyoxymethylene dimethyl ethershaving values of n greater than 1 which mixture is withdrawn from thedistillation column near its bottom.
 12. The process according to claim11 wherein at least a portion of the aqueous side-stream is used forrecovery of an aqueous formaldehyde solution in an adsorption column.13. The process according to claim 6 wherein the acidic catalystcomprises at least one member of the group consisting of bentonite,montmorillonite, cation-exchange resins, and sulfonated fluoroalkyleneresin derivatives.
 14. The process according to claim 6 wherein theacidic catalyst comprises at least one cation-exchange resin of thegroup consisting of styrene-divinylbenzene copolymers, acrylicacid-divinylbenzene copolymers, and methacrylic acid-divinylbenzenecopolymers.
 15. The process according to claim 6 wherein the acidiccatalyst comprises a sulfonated tetrafluoroethylene resin derivative.16. The process according to claim 6 wherein the at least a portion ofthe overhead stream containing dimethyl ether is recycled to thecontacting with the condensation-promoting catalyst of claim
 1. 17. Theprocess according to claim 2 which further comprises formation of thesource of formaldehyde by a process comprising continuously contactingdimethyl ether in the vapor phase with a catalytically effective amountof a catalyst consisting of copper, zinc and a member selected from thegroup consisting of sulfur, selenium and tellurium as catalystcomponents at elevated temperatures to form a gaseous dehydrogenationmixture comprising formaldehyde, dimethyl ether, dihydrogen and carbonmonoxide; cooling the gaseous dehydrogenation mixture with an adsorptionliquid and adsorbing formaldehyde therein; and separating the resultingliquid source of formaldehyde from a gaseous mixture comprisingdihydrogen and carbon monoxide.
 18. The process according to claim 17wherein the catalyst comprises copper, zinc and selenium or tellurium ascatalyst components in an atomic ratios of 1:0.05-0.5:0.01-0.5 with theproviso that the amount zinc is at least equal to the amount of seleniumor tellurium present in the catalyst, and wherein the elevatedtemperatures are in a range from about 500° to about 750° C.
 19. Theprocess according to claim 17 wherein the catalyst comprises copper,zinc and selenium as catalyst components in an atomic ratios of1:0.05-0.5:0.05-0.4 with the proviso that the amount zinc is at leastequal to the amount of selenium present in the catalyst, and wherein theelevated temperatures are in a range from about 600° to about 700° C.20. The process according to claim 17 wherein the resulting liquidsource of formaldehyde contains about 30 to about 85 percent by weightformaldehyde in methanol solution containing less than 5 percent waterby using at least one continous adsorption column with cooling totemperatures in a range downward from about 100° C. to 25° C.
 21. Theprocess according to claim 17 wherein the elevated temperatures aremaintained in a range from about 600° to about 700° C. using a source ofheat derived at least in part from the gaseous mixture comprisingdihydrogen and carbon monoxide by combustion thereof.